Solar struggles: Stirling Energy Systems files for bankruptcy

Solar thermal company Stirling Energy Systems has filed for bankruptcy, according to Renewable Energy World. In contrast to the recent bankruptcies of solar photovoltaic players SpecraWatt, Solyndra and Evergreen Solar, Stirling Energy Systems developed solar concentrators based on stirling engines, which use the sun’s heat to produce electricity, and planned to build projects to sell the power to utilities.

Stirling Energy Systems has been struggling for a while, and lost out on most of two solar projects it had previously lined up. California regulators approved two of Stirling Energy System’s solar projects totaling 1372.5 MW last year, but Stirling Energy System’s sister company, developer Tessera Solar, subsequently sold those projects off to different buyers when it wasn’t able to line up the financing to build them. Utility Southern California Edison, which signed a deal to buy the power in 2005, canceled its contract with one of the projects.

Tessera Solar sold off one project to K Road Power, who has since said it plans to use stirling engines only for a small portion of its project. Another buyer, AES Solar Power, has said it will use solar panels for its project instead of stirling tech. San Diego Gas & Electric told us it canceled the contract to buy power from the AES’s project in spring this year.

As with the bankruptcies of the solar PV makers, the dropping price of silicon and solar cells played a role here, too. Some project developers are turning to solar PV as a more attractive and cheaper option for utility-scale solar plants compared to solar thermal technology. For example, last month Solar Trust of America, which has been developing a 1 GW solar farm in California, announced it will use PV instead of solar thermal technology for the first 500 MW of its project.

Stirling engines have long been thought of as a promising technology to build solar farms, but the matchup has yet to become as popular as other types of solar thermal technologies and solar panels. Stirling Energy Systems developed a 25-kilowatt stirling engine system, which included a giant parabolic dish of mirrors that concentrate sunlight to heat up hydrogen gas inside what’s called a “power conversion unit.” The unit runs a 4-cylinder engine that in turn drives a generator to produce electricity.

One of the big losers in this bankruptcy is Irish firm NTR, which came to the rescue of Stirling Energy Systems in 2008 and invested $100 million for a 52-percent stake in the company. Boeing has also said it planned to partner with the company to develop Boeing’s high-concentration photovoltaic (HCPV) solar power technology.